Abstract : For an eighteenth-century merchant, the ultimate crisis was war; armed conflicts disrupted trade both practically, by subjecting the goods transported to confiscation by the enemy, and financially, by threatening the national and international credit networks and compensation systems on which merchants relied to clear their transactions. This was especially true for French merchants active in the transatlantic trade, when confronted with a war with Great Britain at mid-century. Land-based goods or goods transported along the coast overt short distances could be rerouted, go through intermediaries, or be smuggled in a variety of ways. But by 1750, British domination of the seas was a well-established reality, and the French Navy, weakened by years of political neglect, was unable to protect the approach either to France's major ports, or to the North American continent. As a result, the French trader specialized in importing colonial products (sugar, coffee, indigo, or tobacco come to mind) in an Atlantic port was faced with daunting challenges. This paper shows how large merchants could face the risks of war with considerable efficiency, combining, inside information, international networks, and local control of market segments; The oligopolistic nature of early Modern markets is fully revealed by these processes, which also show how information was kept even from principals outside merchant circles.